The For Loop

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# 6. The For Loop

The for loop enables us to iterate over a sequence of numbers and repeat the same set of operations for each number.

For example, the following program prints all the numbers from 1 to 100:

    for $i (1..100)
    {
        print $i, "\n";
    }

Some explanations about the syntax:

1. `$i` is the iteration variable. It receives the value 1, then the value 2, then 3 and so forth until it is equal to 100, afterwards the loop terminates.
2. The curly brackets (`{ ... }`) encapsulate the loop block. The loop block is executed once for each value `$i` accepts. Within that block, called the loop body, you can use `$i` and you'll get its current value.

We can nest loops, so for example the following program prints the multiplication board:

    for $y (1 .. 10)
    {
        for $x (1 .. 10)
        {
            $product = $y*$x;
            # Add as much whitespace as needed so the number will occupy
            # exactly 4 characters.
            for $whitespace (1 .. (4-length($product)))
            {
                print " ";
            }
            print $product;
        }
        # Move to the next line
        print "\n";
    }

You may have noticed the program's comments. In perl comments start with the sharp sign (`#`) and extend to the end of the line. Writing the multiplication boards with the labels that indicate which numbers are being multiplied is left as an exercise to the reader.

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